1. Field of the Invention
The present invention relates to the improvement of the molding method of unfired ceramic body.
2. Prior Art
In recent years, a number a ceramic bodies have been applied to mechanical components such as an engine and gas turbine, structural members of a chemical plant and the like, and in addition also to ornamental parts of a watch, accessories and the like.
However, many of the engine mechanical components, plant stractural members and ornamental parts have complicated three dimentional structures. In spite of the fact that ceramic materials are superior in heat resistance, corrosion resistance and abrasion resistance, have a higher strength and comparatively light weight, they have difficulty in machining performance, especially in acquirement of molded body having a shape of the three dimensional structure. For acquirement of complicately shaped ceramic body as aforementioned, it was general practice to obtain a desired shape and dimentions by forming an unfired ceramic body before firing by the press molding method, rubber press molding method and the like, and to machine them both before and after the firing the ceramic body.
However, such methods had difficulty in mass production of products having a shape of complicated three dimentional structure, and this had made the costs of the products remarkably higher, thus having made the actual application of various types of ceramic body difficult. So, as the molding method, the following molding methods have been conventionally conducted: the casting molding method wherein a ceramic slurry is cast into a plaster mold to obtain a molded form by utilizing the slip adjacent to the mold and water absorption thereof; the casting molding method wherein said ceramic slurry is cast into a water nonabsorbing mold held being heated at a temperature higher than the caking temperature of the ceramic slurry, then the mold is cooled at a temperature lower than the caking temperature of the ceramic slurry to obtain a molded body or the cast molding method wherein ceramic raw material powders and organic substances are mixed at a high temperature, a flowability is given to make a plastic status, then the mixtures is pressure-cast into a metal mold, thereby molding a ceramic body. (Refer to the patent application laid open NO. 62-257807, patent application laid open NO. 62-289347, patent application laid open NO. 63-30202.)
On the other hand, the cast molding method has generally aimed at acquirement of a shape having a shape having a complicate three dimensional structure by adopting a properly allocated combination type for said mold without distinction of the type of water absorption or non-water absorption of the mold. However, the deflection strength of molded bodies acquired by pouring the ceramic slurry is very low, 2 kg/cm.sup.2 .about.3 kg/cm.sup.2 or less, and a cracking easily generates on the molded body during taking it out of the mold. Especially the plaster mold of water absorption type has a limit on the dimension accuracy of the mold itself. In addition, if the thickness of the molded form is 1 mm or less, it is impossible to fill the mold with the ceramic slurry even by pressure-casting of the ceramic slurry. So the cast molding method had a weak point in that it was difficult to obtain a high accuracy molded body having no internal defect and molded ceramic body having a shape of thin and complicate three dimensional structure.
The cast molding method wherein the water non-abosorption mold is heated and cooled, also had a weak point in that a heating device and cooling device had to be added to the cast molding device, this made a large type and complicate device, in addition, it took much times to control the heating and cooling of the mold at a correct temperature, and the numbers of molded products per unit time was remarkably small, thus resulted in that the molding efficiency was bad and less reliable molded body could be mass-produced.
On the other hand, the injection method has the following many defects: It can not obtain a fluidity allowing ceramic body to be pressure-cast without addition of a greater amount- 20.about.30 weight % of organic binders to ceramic powders. Therefore, after molding, this method requires a binder removal process for a very long time for removal of the added organic binders. In addition, the raw density of the molded body is 60% or less- lower, compared that of the fired product, the firing shrinkage is greater and the deformation rate during the shrinkage is also greater.
This method had also the following disadvantages: As the molding materials to which a fluidity was given by using ceramic raw material powders and organic binders is cast under a high pressure into a mold, the cylinder, nozzle of the injection device and the mold are remarkably abraded, the abraded mold components is mixed into the ceramic raw material powders, thus resulting in that the characteristics of the ceramic body are deteriorated after firing the body.